Distribution of the Oregon Spotted Frog (Rana pretiosa) has shrunk markedly, and more than two-thirds of known populations are located along the Cascade Range in central Oregon. Despite conservation concern, little is known about how habitat attributes and stressors such as invasive species influence R. pretiosa populations. We used egg mass counts to study R. pretiosa habitat relationships at oviposition sites and breeding ponds. Oviposition sites were in shallow water above gradually sloping substrates that supported moderate or dense herbaceous vegetation. Sixty-one per cent of occupied breeding ponds had fewer than 20 egg masses. We found strong support for 2 predictors of egg mass count: positive effect of other R. pretiosa breeding sites nearby, and a negative effect of non-native fish having access to preferred R. pretiosa overwintering habitat. We found moderate support for effects of emergent and submergent vegetation coverage (positive), and of ponds being located in the Klamath River Basin (negative). Maintaining and restoring overwintering habitats that are free of non-native game fish is likely to benefit R. pretiosa in our study area. Further work on movement ecology is needed to improve our understanding of habitat connectivity and the effects of site isolation on the persistence of R. pretiosa in Oregon.
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